Pulmonary embolism (PE) is a sudden blockage in a lung artery due to an embolus that is formed in one part of the body and travels to the lungs in the bloodstream through the heart. It is a common cardiovascular emergency with about 600,000 cases occurring annually and causing approximately 200,000 deaths in the United States. Most patients who succumb to PE do so within the first few hours following the event.
A major clinical challenge, particularly in an emergency department (ED), is to quickly and correctly diagnose patients with PE and dispatch them to the proper treatment, so that hazardous yet life-saving therapy can be prescribed appropriately. Unfortunately, PE is among the most difficult conditions to diagnose. The primary symptoms are protean and may be manifested by a number of other conditions that require different therapeutic interventions. The correct PE diagnosis may be overlooked in as many as 84% of cases, resulting in many preventable deaths.
CT pulmonary angiography (CTPA) is the current diagnostic standard for suspected PE. It reveals embolus as a dark region residing in bright vessel lumen. Each CTPA scan consists of hundreds of axial images. The interpretation of these images is complex and time consuming because of the intricate branching structure of the pulmonary arteries, the demand for specialized knowledge to distinguish PE from the various causes of cardiopulmonary pathology that may resemble PE, and a myriad of artifacts that may obscure or mimic emboli, such as flow-related artifacts, streak artifacts, lymph nodes, etc. The accuracy and efficiency of interpreting such large 3-D image datasets is further limited by human factors, such as attention span and eye fatigue. Incorrect CTPA interpretations are not infrequent in clinical practice. The number of CTPA examinations has increased by an order of magnitude over the past decade, while the rate of true positive examinations has fallen to just 5-10%. There is thus a critical need to mitigate rapidly mounting radiologist workloads and improve the efficiency and accuracy of PE diagnosis in CTPA.